The invention concerns a hydraulic control valve to control a piston with a piston rod on one side with a double-acting working cylinder, whereby the control valve constructed in the piston-moving structure has at least four external connections with ring channels form in the valve housing, namely a pump connection (P), a connection (A 1) for a feed line to and from the large stroke space of the working cylinder, a connection (B) for a feed line to the small stroke space of the working cylinder, and a tank connection (T1) connected to the tank and whereby the control piston of the piston collar of the control valve has control edges arranged on It. through which the connections (P, A1, B, T1) can be connected to one another in both positions of the control piston in such a way that during the work stroke of the working cylinder, a back feed of the fluid forced out of the small stroke space into the large stroke space of the working cylinder takes place as the piston rod is moved out and a connection of the small stroke space to the tank can be switched on for stroke-independent switching of the working cylinder from the work stroke when moving slowly, with a subsequent standing state to release the pressure of the small stroke space of the working cylinder
A control valve with the above-mentioned characteristics is described in DE 10 2008059 436 83. The construction of the control valve should make possible a movement of the piston of the working cylinder with a differential effect, that is, a fast piston movement is envisioned, in which a back feed of the fluid forced out of the small stroke space of the working cylinder during the work stroke of the differential cylinder is envisioned, i.e. ,when the piston rod is moved out, so that the pump must deliver only the same supply quantity both during the work stroke of the working cylinder and during its back stroke with each insertion of the piston rod. To implement his back feed, a fifth internal ring channel is formed in the valve housing of the known control valve, which channel is connected through internal bridges formed in the valve housing to the ring space belonging to connection A. In the working position of the control piston during a back stroke, connection 8, which is connected to the small stroke space of the working cylinder, is connected to the ring channel belonging to connection A through the fifth ring channel and the internal bridges connected to it, so that the fluid forced out of the small stroke space is led to connection A and from there to the large stroke space of the working cylinder.
In addition, in the control valve known from DE 10 2008 059 436 B3, a control function is already achieved that, at least at the end of the working stroke, with the piston rod pulled almost completely out, the full force made available by the pump is no longer used to move the piston, but is used as a holding force. For this, in the control valve known from DE 10 2008 059 436 B3, it is envisioned that the housing-internal bridges leading away from the fifth internal ring channel to the ring spaces belonging to both connection A and to the tank connection are closed, whereby in a connection hole designed for this between the housing-internal bridges and the ring space belonging to connection A, a valve-internal check valve with a pass-through device directed to connection A and in the section of the housing-internal bridges leading to the ring space belonging to the tank connection in the connection hole going upstream from the housing-internal bridges, an externally controllable lock valve to open and close the connection from the internal ring channel to the tank connection T are arranged. If a switch is now made from the rapid piston movement with back feed to the full holding force, then by switching the valve-internal lock valve from its lock position to its open position, the connection between connection B and connection T is opened. With this, the additional back feed of fluid forced out of the small stroke space of the working cylinder is interrupted and the small stroke space is released directly to the tank, so that the pressure acting on the large surfaces of the piston of the working cylinder in the large stroke space is not longer counteracted by pressure in the small stroke space of the working cylinder, and accordingly the holding force against the state while the piston rod is moving out is in any case doubled by the symmetric design of the working cylinder.
In a control valve of this kind, the problem results that during the work stroke of the working cylinder, the fluid forced out of its small stroke space during the entire work stroke is directed over the same control edges of the control piston from B to A 1 or T1. While during the rapid piston movement of the control piston a correspondingly larger volume stream is forced out of the small stroke space and through connection B and the associated control edges from B to A1 into the large stroke space, this volume stream during the holding place or during the transition to it is clearly lower, so that for this work phase of the working cylinder, the control edges from B to A 1 are designed too large The invention is therefore based on the task of providing a control valve designed for different phases during the work stroke, namely during rapid forward movement of the piston and during the subsequent holding phase, according to the generic characteristics, so that the hydraulic tension of the working cylinder is adapted through the control to the volume stream flowing at each time.
The solution of this task, including advantageous embodiments and further developments of the invention can be seen from the content of the patent claims attached to this description.
The invention envisions, in its basic thought, that on a control valve with at least three piston collars with five control edges formed on it, two separate line paths for the fluid forced out of the small stroke space during the work stroke of the piston are established, of which the first, a line path formed as a back feed for the supply and discharge line connected to the small stroke space through a recess acting as a back-feed edge connected to the large stroke space of the working cylinder and the second, a line path formed to connect the small stroke space to the tank, a line path formed to connect the small stroke space to the tank, leads through a pressure-release control edge formed on an assigned piston collar of the control valve, whereby the recess in the assigned control piston is for the fluid stream forced out of the small stroke space of the working cylinder during slow movement and is designed to be smaller than the other recesses of the piston collar formed for the other control edges.
An advantage of the present invention is that the work phase of holding the piston with full holding force now is arranged with a smaller control edge corresponding to a lower volume stream on the piston collar, through which an exact hydraulic tension for the working cylinder is ensured during all work phases. Switching with the lock valve that is still required is all simpler to achieve than the use of the path valve envisioned in the state of the art.